PLANS for a career comeback by singer Sinead O'Connor have been dashed after she cancelled her entire 2012 tour and claimed to be leaving the music business.

The 45-year-old had been enjoying critical acclaim for her latest album 'How About I Be Me (And You Be You)?' but plans to promote the record worldwide, including a 12-date North American tour, have been shelved on the advice of doctors.

"With enormous regret I must announce that I have to cancel all touring for the year as I am very unwell due to bipolar disorder. As you all know I had a very serious breakdown between December and March and I had been advised by my doctor not to go on tour but didn't want to 'fail' or let anyone down as the tour was already booked to coincide with album release.

"So very stupidly I ignored his advice to my great detriment, attempting to be stronger than I actually am. I apologise sincerely for any difficulties this may cause," Ms O'Connor wrote on her website.

The mother of four made the announcement while on tour in Germany, and claimed to be seeking a job outside the music business.

"Asking about jobs as music biz is very bad for Sinead. Any one have a job for a very clever woman with massive heart and courage, who adores people and has to escape music business as is very bad for her? Too much and too many long times away from home. All bad triggers for a woman with a mental illness. Can anyone come and take me home from Munich?," Ms O'Connor tweeted before cancelling a date in the German city on Saturday night.

Last night she remained adamant about leaving the music business, announcing that she was closing her Twitter account.

"This account will close tonight for reasons of wishing to be out of limelight and showbiz. Shall reappear anonymously. Midnight is close down. Goodnight, thank u, u been a wonderful audience. X" she tweeted. Her website sineadoconnor.com was also offline.

The singer was unavailable for comment when contacted last night.

Hailed by fans and critics alike, her new album 'How About I Be Me (And You Be You)?' peaked at 33 in the UK charts.

Last month the singer revealed her marriage to drugs counsellor Barry Herridge, who she wed in Las Vegas in December, was over.